In the prior art, in a tire for heavy load such as an off-the-road-radial (ORR) tire and a truck and bus radial (TBR) tire, rubber on a tire side section, in particular, rubber on a bead section side is apt to be deformed by friction with a rim flange and thrusting up from the rim flange. In order to reduce such deformation, a method of increasing thickness of the rubber on the tire side section, in particular, the rubber on the bead section side is employed. However, if the thickness of rubber is increased, heat is likely to be generated by the deformation of the rubber. The heat generation in the tire side section promotes degradation of the rubber, leading to deterioration of durability of a tire, and therefore, a tire which reduces a temperature increase in the tire side section has been desired.
In order to solve such a problem, there has been proposed a method of providing a turbulence-generating protrusion, which projects outward in a tire width direction from an outer surface of the tire side section, in a portion of the tire side section to generate turbulence of air on the outer surface of the tire side section, and, thus, to reduce the temperature increase (for example, see Patent Literature 1).
In tires for heavy load, since thickness of rubber in a tire side section is larger than thickness of a tire for passenger car, although the provision of the turbulence-generating protrusion gives a cooling effect on an outer surface of the tire side section, an inside of the tire cannot be cooled, so that the effect of reducing the temperature increase may not be obtained 14 sufficiently.
Thus, in recent years, there has been considered that a circumferential recessed section depressed inward in a tire width direction is formed in a portion of a tire side section along a tire circumferential direction, and, at the same time, a turbulence-generating protrusion is provided in a region where the circumferential recessed section is formed, whereby the temperature increase is more efficiently reduced.